This invention is related to my copending Ser. No. 921,574, filed Oct. 21, 1986, now U.S. Pat. No. 4,839,121, entitled improved High Density Tape Casting System which is hereby incorporated herein by reference.
In the process for the electrolytic separation of oxygen from air, using solid electrolyte membranes such as zirconia, porous electrodes are needed. At present, ceramic electrode material is supplied as a fine powder and it is highly desirable to increase the particle size to increase the porosity of the electrode. However, as the particle size increases, contact area between particles decreases thereby increasing the electrode electrical resistance, an undesireable occurance. An improved porous electrode configuration is therefore needed having interconnecting pores and large contact area between the particles of the electrode material. Such improved porous electrodes can then be used in thin ceramic membrane, commonly called tapes.
Thin ceramic membranes or tapes are typically made from ground ceramic suspended in a mixture of solvents, binders, and other components, to form a slurry which is spread on a flat surface and allowed to cure by air-drying. The flexible, pliable tape is then fired in a kiln to remove solvents and other impurities, and results in a hard ceramic substrate for use in capacitors. Tapes are also formed in multilayer ceramic sandwiches comprising electrodes and insulators for separation of oxygen from air, and for use as the membrane of high temperature solid electrolyte fuel cells and high temperature solid electrolyte electrolysis cells and the like, hereinafter referred to collectively as "tape-containing devices".
Strontium doped lanthanum magnaite, which for brevity is sometimes referred to herein as "LSM", is known to be a good material for use in electrodes produced by tape casting methods. LSM having the mole ratio La.sub.0.8 Sr.sub.0.2 MnO.sub.3 is available as a submicron size material having a surface area of 3 to 5 m.sup.2 /g from HUA Associates, Rolla, Mo.
Eight mole percent yttria stabilized zirconia, which for brevity is sometimes referred to herein as "YSZ", is known to be a good material for use in the electrolyte layer in such tape-containing devices.